The overall objectives of the present research proposal are: (1) to identify naturally occurring compounds that have the capacity to inhibit chemical carcinogenesis, (2) to establish conditions under which inhibition occurs, and (3) to determine the mechanism or mechanisms by which observed inhibitory effects are brought about. The principal focus with regard to investigations of mechanisms of inhibition will be on naturally occurring indoles found in cruciferous plants. These compounds inhibit polycyclic aromatic hydrocarbon-induced neoplasia in rodents. Studies of their effects on polycyclic aromatic hydrocarbon metabolism will be undertaken in an effort to elucidate the alterations which are responsible for inhibition of carcinogenesis. Additional investigations will be carried out to determine if plants other than cruciferae have constituents which alter carcinogen metabolism so as to increase detoxification. If so, attempts will be made to isolate and identify the responsible constituents.